1. Field of the Invention
The present invention is related to the field of tongue-base therapies (particularly as relates to obstructive sleep apnea), and more particularly, to a system and method of predicting the efficacy of tongue-base therapies (particularly for the treatment of obstructive sleep apnea).
2. Description of Related Art
Obstructive sleep apnea (OSA) has been found to be as common as diabetes, asthma, and hypertension. Like those multi-systemic problems, OSA affects a large percentage of the population. However, with proper diagnosis and treatment, patients can live a normal life, and life-threatening risks are reduced.
The prevalence of OSA has been estimated to be 20% in the World's adult (25+ years of age) population (or approximately 660 million), with approximately 7% of all adults (˜230 million) suffering from moderate to severe forms of the condition. The estimated incidence of mild OSA is even larger (estimated ˜400 million). In the USA alone, an estimated 1 in 5 (˜40 million) adults suffer from some form of OSA, with 1 in 15 (˜15 million) adults having moderate to severe forms of OSA. The awareness and diagnosis of OSA are growing. Analysts estimate that fewer than 4% of OSA sufferers are currently diagnosed and being treated. This “undiagnosed patient gap” has created one of the fastest growing segments of the medical device industry, and this percentage is forecast by analysts to increase to over 24% by 2012.
Driving market growth coupled with an aging population (OSA risk increases over 40 years of age) have increased awareness of the public and the media and diagnosis by physicians. OSA is considered a risk factor for stroke and congestive heart failure, indications that are currently being studied in multicenter clinical trials.
There is no known cure for obstructive sleep apnea. Behavioral treatments such as weight loss and alcohol avoidance may be helpful, but are not always completely effective therapies. Surgical procedures are considered second line therapies and current surgical modalities result in inconsistent results. While airway pressure treatment is considered to be the first line of therapy worldwide (and has proven to be the most successful therapy in maintaining an open airway), this form of treatment suffers from a significant incidence of side-effects, and there is an equally significant lack of long-term patient compliance. The competitive environment for OSA therapeutic devices can be segmented into three main categories based upon treatment methods: nasal mask continuous positive airway pressure (CPAP), passive mandibular advancement oral appliances (OAT), and active oral positive airway pressure devices.
For nearly all patients diagnosed with some form of OSA, the most prescribed treatment (80% of all Rx's) is a nasal mask plus air flow generator machine for the delivery of nasal CPAP, variable pressure Bi-level, or Auto-titration (“smart”) CPAP systems to “splint open” the airway allowing air to flow freely to the lungs during periods of airway occlusion. CPAP systems have been found effective in treating mild, moderate, and severe cases of OSA and are considered the gold standard treatment modality.
Problematic to this form of treatment, however, is non-compliance. The American Sleep Disorders association estimated in 1993 that approximately 50% of patients prescribed CPAP systems were non-compliant (i.e., use of CPAP less than 4 hours per night). Non-compliance is the extreme manifestation of patient dissatisfaction with nasal CPAP; even compliant patients are not satisfied, as evidenced by the wide range of problems encountered by all users of nasal CPAP mask systems (e.g., nasal stuffiness, mask leak, dry throat, cold air stream, mask rubbing, more frequent awakenings, red/sore eyes, and nosebleeds).
Major factors in non-compliance are bulkiness, discomfort, and leakage problems inherent in the nasal mask CPAP systems. The number one complaint by OSA patients is the discomfort caused by their nasal mask. Poor training and follow-up from the device distributor, claustrophobia, nasal congestion, discomfort, complications with headgear adjustments, and nasal and skin allergies are also problematic. Excessive sinus irritation, injury, or physical deformities make nasal CPAP impractical. CPAP use is also associated with a limitation on the part of the patient to sleep in varying body positions while connected to the device; CPAP users are required to sleep only on their back or sides (they are unable to sleep in the prone position, i.e., on their stomachs). Patient health, public safety, and economic productivity all suffer when OSA patients fail to comply. All of these factors combined often promote seeking of alternative forms of treatment for this disorder, as described below.
Passive Dental Mandibular Advancement Appliances (OAT) affect advancement of the lower jaw, and are used to reposition the tongue in the oropharyngeal cavity to create a larger air passageway. These devices are useful as a primary treatment in a large percentage of cases of snoring and mild-moderate OSA (and in some isolated cases of severe OSA) and are often useful in cases of persistent apnea following failed soft palate or other upper airway surgery. Sleep physicians, general dentists, oral & maxillofacial surgeons, other dental specialists, and otolaryngologists often prescribe this treatment.
Based upon recent studies, a newly published Practice Parameter Paper produced by the American Academy of Sleep Medicine has added substantial credibility to this form of treatment, as numerous recent Level I and II studies have significantly elevated the level of knowledge surrounding use of these appliances and verified efficacy of this treatment. In particular, the American Academy of Sleep Medicine has revised its previously published practice parameters to now recommend first-line use of oral appliances in mild to moderate OSA (in those patients who prefer oral appliances to CPAP, or who are intolerant to CPAP therapy). Importantly, Level I evidence exists which suggests that OAT therapy is more effective than soft palate surgery in patients with mild-moderate OSA, and it is expected that prescriptions for this form of treatment will increase in the future.
Side-effects of OAT include potential changes in dental occlusion, Temporomandibular Joint symptom exacerbation, and current lack of capability to specifically predict who will respond best to this treatment.
Active Oral Positive Airway Pressure Devices deliver positive pressure airflow via the oral cavity (bypassing the nasal airway). Oral Positive Airway Pressure (OPAP) incorporates mandibular advancement and positive pressure ventilation, while other masks (such as the Oracle mask) deliver positive pressure ventilation alone without incorporating mandibular advancement. Minimal long-term data are available with this technique, and airway drying (despite the use of humidified circuits) is problematic.
Pharmacologic treatments for OSA have been ineffective. The fundamental cause of OSA is anatomically related and not impacted biochemically.
Various surgical techniques have been developed to treat OSA. Uvulopalatopharyngoplasty (UPPP) treatment includes resection of the uvula and portions of the soft palate to widen the oropharyngeal space. Although snoring is temporarily relieved in most cases, apnea often persists due to continued tongue-base narrowing. The overall success rate of UPPP is about 40% for primary snoring, but less for apnea (problematic is that many physicians fail to obtain objective sleep study data either before or following performance of this procedure, and a “silent apnea” situation is often created). Velopharyngeal incompetence and pharyngeal stenosis are significant complications to all forms of soft palate surgery.
Laser-Assisted Uvulopalatopharyngoplasty (LAUP) performs a similar result as the above utilizing a CO2 laser. Laser treatment may worsen the respiratory disturbance index (RDI) and can cause long-term sequelae of a scarred airway. While snoring may be diminished, the diagnosis of OSA may be delayed because the primary symptom of OSA, i.e., snoring, is eliminated.
Genioglossus advancement procedure (GBAT) procedure includes advancing the genioglossus attachment to the mandibular symphysis forward and fixating the same with plates and/or screws. Importantly, the long-term results of this technique are unknown, and clinical data surrounding the use of this technique are limited as it is often performed at the same time soft palate surgery is performed.
Maxillomandibular Advancement (MMA) has proven effective at reducing snoring and OSA in patients that have failed other therapies and who have clear anatomical abnormalities warranting a more intensive intervention. This procedure involves surgical repositioning of the upper and lower jaws. While the surgical literature suggests that this procedure has the greatest impact on affecting volumetric expansion at multiple areas of the upper airway (and is considered the most successful surgical procedure [outside of tracheostomy] for treatment of OSA), changes in facial appearance in addition to cost, complexity, and inconvenience have prevented this procedure from gaining wide acceptance.
Tracheostomy is typically the most effective and definitive surgical therapy for OSA. The oropharynx obstructed in OSA is simply bypassed by creating a hole in the trachea and inserting a tube to maintain a patent airway. This therapy has become less common due to the success of CPAP, and significant social stigma prevents the widespread use of this technique for most patients.
Radiofrequency (Somnoplasty) induces thermal lesions in the palate (for primary snoring) or tongue-base (for patients with OSA) which subsequently scar and resorb. This technique has not proved effective for OSA, as the majority of patients exhibit narrowing below the level at which the lesion is placed, and a relapse of snoring is typically seen 1-2 years following soft palate application in patients with primary snoring.
Injection Snoreplasty and scar-tissue inducing implants, like radiofrequency, induce scarring of the soft palate. While some temporary benefit is seen in patients with primary snoring and milder forms of apnea, recurrence of symptoms is often seen, and little (if any) long-term data is currently available.
Tongue-Suture techniques (Repose) utilize a nonresorbable suspension suture to advance the hyoid or tongue base; little (if any) long-term data related to this technique is currently available.
Clinicians, however, often offer a “shotgun” approach to all-corners with OSA (i.e., oral appliances are fabricated for all-corners), and no specific technique or mechanism is utilized in order to predict a given individual's probability of response to therapy (prior to appliance fabrication and initiation of treatment). As an alternative, clinicians often rely upon resolution of symptoms (after titration has been performed) as a means to judge response to therapy, but this is performed only after the appliance has been fabricated and treatment initiated. Unfortunately, beyond the generalized guidelines listed above, clinicians are currently unable to predict in advance which individuals will uniquely respond to OAT treatment and, therefore, who are the most appropriate candidates for this form of OSA therapy.
Similarly, surgeons involved in performing mandibular advancement (or tongue-base) surgery in patients with OSA currently have no means of predicting how far the mandible (or tongue base) must be advanced in any given individual in order to affect a cure of upper airway obstruction. This inability to predict response to therapy often leads to inappropriate appliance fabrication and/or inappropriate or inadequate surgical advancement in patients who will not, by reasons of anatomical expansion or physiologic improvement, respond to therapy.
While mandibular protrusion/advancement is the basic mechanism implemented by OAT, it is generally accepted that oral appliances work by affecting both anatomic expansion of the tongue-base region and physiologic reduction of soft tissue compliance (of the upper airway) during sleep. While obstruction is accepted to be a dynamic (or non-fixed) process, anatomic expansion in this case (per Poiseuille's Law) refers to the ability to expand the most critical (or stenotic) site of proximal narrowing of the upper airway (MCSPN) above the glottic opening. Per Poiseuille's law, small changes in the radius of the tube at its narrowest point affect exponential changes in airflow (the radius in this equation is raised to the fourth power). For example (all else being equal) according to Poiseuille's law, doubling the radius of the tube at its narrowest point increases airflow by a factor of sixteen.
It would therefore be advantageous to provide a system and method of providing objective data to predict the efficacy of tongue-base therapies, such as various nonsurgical and surgical tongue-base therapies, the response to both OAT treatment, and mandibular advancement surgery in patients with OSA. Moreover, it would be advantageous to provide a system and method for generating such predictions in a user-friendly and reliable manner.